Expanding brake operator



p 1951 P. FARKAS EXPANDING BRAKE OPERATOR 2 sheet s Sheet, 1

Filed May 27, 1946 INVENTOR, fierrelaz'lw;

ATTORNEY.

Sept. 4, 1951 P. FARKAS EXPANDING BRAKE OPERATOR 2 Sheets-Sheet 2 Filed May 2'7, 1946 ATTORNEY Patented Sept. 4, 1951 ()FFICE EXPANDING BRAKE OPERATOR Pierre Farkas, Paris, France Application May 27, 1946, Serial No. 672,516 In France November 18, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires November 18, 1962 Claims. (01. 1ss 7s) The present invention relates to an improved brake of the drum and expanding shoe type,

whether mechanically, hydraulically or pneumatically operated.

A known form of vehicle brake comprises a pair of arcuate shoes pivotally anchored, at one pair of adjacent ends, on a fixed back plate and resiliently biased at their other ends against some form of expander which, when operated either mechanically, serves to pivot the two shoes outwardly against -a -brake drum. Instead of anchoring one pair of ,ends, it is known to articulate these ends together hydraulically or pneumatically,

by a turnbuckle or other adjustable means for separating the shoes at this point so as to compensate for wear of the brake linings.

- One arrangement for expanding the shoes includes a toggle joint consisting of a bell-crank lever articulated to one of the shoes and acting through a link on the other shoe, but in this proposed device both the link and the lever exert their action on the shoes along lines perpendicular to the axis of symmetry of the brake at points relatively far apart on the shoes and the device includes anchorages for the shoes which cause a see-saw action of the latter and hinder their smooth operation.

Having in mind the defects of the prior art brakes it is the object of the present invention to provide improved means for producing smooth and equal braking effects on the two shoes.

With these objects in view, and in accordance .with the present invention, there is provided a wheel-brake including a brake-drum movable with the wheel, a relatively fixed back-plate, primary and secondary brake shoes articulated together at one pair of adjacent ends so as to be expandible aganist the drum, toggle mechanism mounted on the back-plate for expanding the other pair of adjacent ends of the shoes and comprisin a link acting obliquely on the end of the primary shoe and a bell-crank lever exerting "on the secondary shoe both a rearward push and that is to say, the jaw on the forward side of the expander in the direction of rotation, is first brought into contact with the drum whereupon the rotation is effective to wrap this jaw on the drum and to transmit its motion to that end of the -secondary jaw opposite the expandenas a function of the friction on the primary jaw, which then also wraps on to the drum. The toggle mechanism is preferably fully floating and may be mechanically, hydraulically or pneumatically operated.

The rearward and disengaging action of the bell-crank lever on the end of the secondary shoe reduces the pressure of this end of the secondary shoe against the drum and against a fixed abutment located between the ends of the shoes, so that there is produced a differential effect tending to equalize the circumferential action of the two shoes against the drum. Each shoe may be of a plurality of arcuate segments articulated together and touching with point contact only so as to facilitate their conforming to the surface of the drum.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization, and

its method of operation, together with additional objects and advantages thereof, will best be understood from the followin description of specific embodiments, when read in connection withthe accompanying drawings, wherein like reference characters indicate like parts throughout and in which:

Figure 1 is a side view in elevation, partly in section of a mechanically operated brake,

Figure 2 is a cross-sectional view taken on the line IIII of Figure 1,

Figure 3 is a side view in elevation, similar to that of Figure 1, of a hydraulically operated brake;

Figure 4 is a cross-sectional View taken on the line IVIV of Figure 3,

Figures 5 and 6 are fragmentary cross-section- 'al views taken longitudinally and transversely,

respectively, of a hydraulic cylinder such as may be used in the system of Figures 3 and 4, and

Figures '7 and 8 are fragmentary cross-sectional views taken longitudinally and transversely respectively, of a modified form of hydraulic cylinder.

The brake illustrated in Figures 1 and 2 com prises a back plate 20 rigidly secured to a vehicle, a brake-drum 2| fixed to a road wheel of the vehicle, and mounted on the back-plate 20. a pair of arcuate brake-shoes 22 and 23,. a device 24 for adjusting the shoes relative to each other to compensate for wear of the linings of the shoes and on which the shoes are pivoted; a wedgeshaped abutment 25, having radial faces, against which one pair of adjacent ends of the shoes may bear, and a bracket 26 serving to hold and locate a sheathed brake-operating cable 2'! ending in a bifurcated hook 28 engaging a shoe-expanding toggle mechanism.

The toggle mechanism includes a double bellcrank lever 29 connected with the shoe 23 and a double link 30 connected with the shoe 22. The two parts'of the parallel pair of links 30 and 30', best shown in Figure 2, are kept in suitably spaced disposition by a washer 3| mounted on a pin 32 fixed on the back-plate 26. The bifurcated. hook 28 is biased to its upper-most position by a helical spring 33 compressed between a collar 34 on the hook and the bracket 26'.v The double. link 30 is pivotally connected to the shoe: 22' by a) pivot 35 and the shorter arm of the double bellcrank lever 29 is pivotally connected to the other shoe 23 by a pivot 36, the lever and link being pivotally connected together by a pivot 3! to constitute the knuckle of the toggle joint which is operated upon movement of the longer arm of the: bell-crank lever by the hook 28 which. is operated bythe cable 21. It should be noted that the three points of articulation 35, 36 and 31 are fully floating and that the link 30 is oblique to the axis of symmetry II--II of, the brake.

The top adjacent ends of the shoes 22 and 23 are biased against the segmental abutment by a pair of helical springs 38 and 39. The shoes are, preferably, divided into segments which. are adjustably connected at 43 and 4|, so that. they can pivot at these points. The shoes have their lower ends resiliently retained in pivotal contact with the wear-compensating device 24 by a spring 432. The wear-compensating device 24' is such as to permit any circumferential movement of the lower end. of shoe 22 to be transferred to. the shoe 23 and is preferably automatic in operation. In the. operation of the brake, when the brakeoperati'ng cable 21 is pulled the hook 28 is retracted. in the direction of the arrow S. The bell-crank lever 29 swings about pivot. 36. and pushes the link 30, inv a direction oblique to the axis of symmetry, so as to force the upper end of the primary shoe 22 against the drum in the direction 1'. As the link swings about pivot in clockwise direction, the thrust of the shoe 22 against the drum approaches its extreme upper end. At the same time, the bell-crank lever 29, swinging about pivots 36 and 31 tends, simultaneously, to push the secondary shoe 23 in the direction u and to withdraw its upper end away from thedrum in the direction 15.

Assuming the drum to be rotating in the direction of arrow A, it will be seen that shoe 22 end, against the drum whereupon the action of this shoe is also self-wrapping.

It is to be particularly noted that, although shoe 23 is also self-wrapping, starting from its lower end, its upper end. is not jammed against the abutment 25 because the bell-crank lever 29 holds it away from the abutment. ping action thus, as it were, commences at the upper end of shoe 22', and the several sections of the two shoes wrap themselves against the drum in anti-clockwise, sequence right around the 'drum, up to the upper end of shoe 23.

lhe modified. devices illustrated in Figures 3 to 8 operate upon the same principle as that of Figures 1 and 2,-but the mechanical control is replaced by hydraulic control. Pivoted on, the

Self -wrapshoe 22 by a pivot 43 is a piston 44 working in a. cylinder 45, a seal between the piston and cylinder being provided by a cup washer 45 biased against the piston by a spring 4! under compression between the piston and cylinder, as best shown in Figures 5 and 7. Pivoted on the shoe 23 by a pivot 48 is a bell-crank lever 49 provided with a lug or spur 50 and having threaded through its lower end an adjustable screw 5!, the end of which bears against the outer end of the cylinder, in a socket formed therein.

Fluid under pressure can be admitted and withdrawn from the cylinder 45, above the piston, by way of a pipe 52, as shown in Figures 5 and '7. A bleeder duct 53 leads toa bleeder hole closed by a plug 54 screwed to the outside of the housing 20 as shown in Figure 6, or inside the housing as shown in Fig. 8. The washers 55 and 53 and a spring 5'! (Figure 4) locate the device laterally, but permit movement across the housin 20.

The" hydraulic mechanism is operated upon actuation of the usual brake pedal or lever (not shown) which serves to force fluid under pressure through pipe 52- into the cylinder 45 thus urging the piston 44 towards shoe 22 and urging the cylinder 15 towards shoe 23'. But, while the shoe 22 is moved towards the drum 2f in a. direction oblique to the axis IV'IV, the effect of the spur 58 on the bell-crank lever is to cause the upper end of the shoe 23 to be moved approximately tangentially downwards. In other words, this end is moved, as it were, downwards and around the inside of the drum with a slight movement away from the drum.

Assuming, the drum to be moving in the direction of the arrow A, the shoe 22 wraps on to the drum, from its upper end downwards, and is also movedslightly downwards. This anti-clockwise shift is transferred through the wear-compensating device 24 to the lower end of shoe 23 which thereupon wraps on to the drum from its lower end upwards. It will be noted that, as before, the'bell-crank: lever serves to hold the upper tip of shoe 23' away from the abutment 25.

The hydraulic piston and cylinder illustrated in Figures I and 8 are similar to that of Figures 5 and 6 except that the supply line 52 and the bleeder plug 54 are attached to the cylinder 45 in simpler fashion.

It will be appreciated that, in. all of the devices described, the shoes exert pressure on practically the'whole peripheral surface of the drum. since the fixed abutment 25 can be made verysmall, and the equal smooth. application. and self-wrapping effect is rendered possible by virtue of the fact that the shoes have no anchorages at theirupper ends. I

Although a certain specific embodiment of. the invention has been shown and described, it is obvious that many modifications thereof arev possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit'of the appended claims. Having thus described my invention, what I claim and desire to secure by Letters; Patent is:

1; Abrake comprising a movable brake-drum, a relatively fixed back-plate, primary and secondary brake shoes articulated together at. one pair of their adjacent ends. so as to be expand-ible against the drum, toggle mechanism for expanding the other pair of adjacentends of the shoes and mounted. on the back-plate, said toggle mechanism including a. link connected at one end direotly to the end of the primary shoe to act obliquely outward thereon and pivotally connected at the other end to a bell crank lever which is pivotally connected directly to the secondary shoe to exert both a rearward push and a disengaging movement, and means for expanding the toggle mechanism.

2. A brake comprising a movable brake-drum, a. relatively fixed back-plate, brake-operating means mounted on the back-plate, primary and secondary shoes articulated together at one pair of their adjacent ends so as to be expandible against the drum, said shoes each comprising a plurality of segments that are adjustably connected in end-to-end relation, a fixed abutment between the other pair of adjacent shoe-ends, spring means biasing said latter pair of adjacent shoe-ends respectively toward said abutment to retract and center said shoes, and toggle mechanism for expanding the shoe-ends adjacent the abutment and including a link and a bell-crank lever, said link being pivoted at one end on the primary shoe adjacent the abutment so as to be oblique to the axis of symmetry of the brake and upon actuation to exert an obliquely outward pressure on said shoe and its segments against said brake drum, said link being pivotally connected at the other end to the knuckle of the bell crank lever, said bell-crank lever having one arm pivoted directly to the secondary shoe adjacent the abutment and the other arm connected with the brake operating means.

3. A brake comprising a movable brake-drum, a relatively fixed back plate, brake-operating means mounted on the back plate, primary and secondary shoes articulated together at one pair of their adjacent ends so as to be expandible against the drum, a fixed abutment between the other pair of adjacent shoe-ends, said abutment having lateral side faces that are radial of said drum for engagement by said shoe-ends, spring means biasing said latter shoe-ends respectively against said lateral abutment faces to retract and center said shoes relative to the brake drum, toggle mechanism for expanding the shoe-ends adjacent the abutment and including a link and a bell-crank lever, said link being pivoted at one end directly on the primary shoe adjacent the abutment so as to be oblique to the axis of symmetry of the brake and upon actuation to exert an obliquely outward pressure on said shoe against said brake drum, said link being pivotally connected at the other end to the knuckle of the bell crank lever, said bell-crank lever having one arm pivoted directly to the secondary shoe adjacent the abutment and the other arm connected with the brake operating means, and guides floatingly mounted on the back plate for holding the toggle mechanism in correct lateral position of the back plate but permitting peripheral floating thereof.

4. A wheel-brake including a movable brake drum, a relatively fixed back-plate, primary and secondary brake-shoes articulated together at one pair of adjacent ends so as to be expandible against the drum, a fixed abutment mounted on the back plate between the other pair of adjacent ends of the shoes, toggle mechanism for expanding the shoe-ends adjacent the abutment comprising a bell crank lever and a piston and cooperating cylinder, said bell crank lever having one arm pivoted on the secondary shoe and the other arm articulated to one end of the piston and cylinder, the other end of said piston and cooperating cylinder being articulated to the primary shoe adjacent the abutment and brake operating means for controlling the flow of fluid to and from the cylinder.

5. A brake as defined in claim 4, wherein the axis of the piston and cylinder is oblique to the axis of symmetry of the brake.

PIERRE FARKAS.

REFERENCES CITED UNITED STATES PATENTS Name Date Dodge Apr. 2, 1935 Number 

